20 



THE CRUSTACEA 



so-called " otocysts " is connected with the equilibration of the 

 body. They are more properly, therefore, termed " statocysts." 



Another modification of sensory setae is believed to be 

 associated with the sense of smell. In most Crustacea the 

 anntenules and often also the antennae bear groups of hair-like 

 filaments, sometimes slender, sometimes more or less swollen, in 

 which the cuticle is extremely delicate. These are known as 

 olfactory filaments or aesthetascs (Fig. 14, A, B). They are often 

 more strongly developed in the male sex, and are believed to guide 

 the males in pursuit of the females. 



FIG. 14. 



A, antenna of Daphnia magna bearing a group of "olfactory filaments." gr, nerve-ganglion 

 sending fibrils to the olfactory filaments. B, one of the filaments further enlarged. (After 

 Scourfield.) C, "auditory" seta from peduncle of antennule of Mysis rdictu. (After Sars.) 



Glands. Apart from the digestive and excretory glands already 

 mentioned, and from other glandular structures to be described in 

 connection with the reproductive system, many Crustacea possess 

 dermal glands scattered over the surface of the body and limbs 

 or grouped at certain points for the discharge of special functions. 

 These consist of single cells or groups, traversed by ramified intra- 

 cellular canals, and communicating with the exterior by fine ducts. 

 Such glands occurring on the walls of the oesophagus or in the 

 neighbourhood of the mouth have been regarded as salivary in 

 function. Others on the surface of the body and limbs may be 

 used, as in some Amphipoda, for the construction of tubular cases 

 or nests in which the animals live, or, as in some Copepoda, may 

 secrete a gelatinous envelope enabling the animals to survive dessi- 



